Pathogenic bacteria are a substantial cause of sickness and death in both humans and animals. One of the most prominent gram-positive organisms among these is Staphylococcus aureus (S. aureus). Infection with these cocci often results in the development of a superficial abscess. Other cases of S. aureus infection are more serious. For example, intrusion of S. aureus into the lymphatics and blood, can lead to a systemic infection which, in turn, can cause complications such as endocarditis, arthritis, osteomyelitis, pneumonia, septic shock and not uncommonly death.
A prominent gram-negative bacterial pathogen is Pseudomonas aeruginosa (P. aeruginosa). These rod-shaped bacteria can infect skin and soft tissue, and critical organs such as the lungs, urinary tract, and kidneys. They can also cause septic shock. As with S. aureus, P. aeruginosa infection often occurs in immunocompromised or hospitalized patients. These patients are frequently colonized or infected with both S. aureus and P. aeruginosa—a condition which might exacerbate infections with either. See Hoffman et al., Proc. Nat'l Acad. Sci. USA, 103:19890-19895, 2006.
The standard treatment for bacterial infections has been antibiotic therapy. Unfortunately, over the last several decades, several pathogenic strains of bacteria have developed resistance to various antibiotics. Worse, some of these strains have acquired resistance to multiple antibiotics.